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United States Patent |
5,679,860
|
Haas
,   et al.
|
October 21, 1997
|
Process for the production of 3-aminoethyl-3,5,5-trimethylcyclohexyl
amine
Abstract
A process for producing 3-aminomethyl-3,5,5-trimethylcyclohexyl amine
(isophorone diamine) from isophorone nitrile. Isophorone nitrile is
iminated in a first stage and then the reaction mixture is subjected to
aminating hydrogenation in a second stage in the presence of a fixed bed
hydrogenation catalyst based on Raney cobalt. The fixed bed hydrogenation
catalyst is produced in a special manner by mixing a powdery
Co--containing Raney alloy with powdery cobalt, sintering the powdery
mixture to shaped moldings and then activating by leaching with alkali
hydroxide solution. The yield and/or space-time yield in isophorone
diamine production can be increased.
Inventors:
|
Haas; Thomas (Frankfurt, DE);
Burmeister; Roland (Geiselbach, DE);
Arntz; Dietrich (Oberursel, DE);
Weber; Karl-Ludwig (Dieburg, DE);
Berweiler; Monika (Maintal, DE)
|
Assignee:
|
Degussa Aktiengesellschaft (DE)
|
Appl. No.:
|
739044 |
Filed:
|
October 28, 1996 |
Foreign Application Priority Data
| Oct 30, 1995[DE] | 195 40 191.3 |
Current U.S. Class: |
564/448; 564/461 |
Intern'l Class: |
C07C 209/32; C07C 209/48 |
Field of Search: |
564/448,461
|
References Cited
U.S. Patent Documents
3352913 | Nov., 1967 | Schmitt et al. | 260/563.
|
3558365 | Jan., 1971 | Duddy | 136/120.
|
3781227 | Dec., 1973 | Sokolsky et al. | 252/466.
|
4826799 | May., 1989 | Cheng et al. | 502/301.
|
5091554 | Feb., 1992 | Huthmacher et al. | 558/341.
|
5504254 | Apr., 1996 | Haas et al. | 564/446.
|
5536694 | Jul., 1996 | Schuetz et al. | 502/301.
|
Foreign Patent Documents |
0 091 027 | Oct., 1983 | EP.
| |
0 042 119 | Mar., 1984 | EP.
| |
0 394 967 | Oct., 1990 | EP.
| |
0 449 089 | Oct., 1991 | EP.
| |
2 100 373 | Sep., 1972 | DE.
| |
2 139 774 | Apr., 1973 | DE.
| |
2 101 856 | Oct., 1973 | DE.
| |
2 053 799 | Jun., 1974 | DE.
| |
28 29 901 | Jan., 1990 | DE.
| |
44 26 472 | Feb., 1995 | DE.
| |
Other References
JP Patent Appln. Disclosure 7-188126--Jul. 25, 1995.
JP Patent Appln. Disclosure 6-321870--Nov. 22, 1994.
JP Patent Appln. Disclosure 99 987/75--Aug. 8, 1975.
|
Primary Examiner: O'Sullivan; Peter
Attorney, Agent or Firm: Beveridge, DeGrandi, Weilacher & Young, L.L.P.
Claims
We claim:
1. A process for producing 3-aminomethyl-3,5,5-trimethylcyclohexyl amine
from 3-cyano-3,5,5-trimethylcyclohexanone comprising in a first stage,
converting said cyclohexanone in an imination reaction with ammonia at
least partially into 3-cyano-3,5,5-trimethylcyclohexane imine, to form a
first reaction mixture
and in a second stage, after the addition of an alcohol with 1 to 3 carbon
atoms, subjecting said first reaction mixture to aminating hydrogenation
with hydrogen in the presence of a fixed bed hydrogenation catalyst at at
a temperature in the range from 50.degree. to 150.degree. C. and a
pressure in the range from 3 to 10 MPa,
wherein said hydrogenation catalyst is produced by a process comprising:
(i) intimately mixing at least one powdery cobalt alloy and powdery cobalt
as binder to obtain a powdery mixture, wherein the cobalt alloy contains
cobalt and optionally promoters as well as a leachable alloy component
selected from the group consisting of aluminum, zinc and silicon, and said
powdery mixture contains cobalt and said leachable alloy components in the
ratio by weight of between 30 and 70 and 75 to 25,
(ii) sintering said powdery mixture to form a mechanically stable molding
with a density of 1.3 to 5.5 g/cm.sup.3, a pore volume of up to 0.5
cm.sup.3 /g (water adsorption) and a BET surface area (DIN 66 132) of less
than 1 m.sup.2 /g and
(iii) activating the sintered molding by at least partial leaching out of
said leachable alloy component by means of an alkali hydroxide solution.
2. The process according to claim 1 further comprising converting said
cyclohexanone in the presence of an imination catalyst.
3. The process according to claim 2, wherein said imination catalyst is a
member selected from the group consisting of acid oxides, zeolites, acid
ion exchangers and supported heteropoly acids.
4. The process according to claim 1 wherein said imination reaction is
carried out in the presence of a C.sub.1- to C.sub.-3 alcohol.
5. The process according to claim 3, wherein said imination catalyst is
used in the form of mechanically stable moldings in a fixed bed reactor.
6. The process according to claim 1 wherein said fixed bed hydrogenation
catalyst is arranged in a hydrogenation reactor and the reactor is
operated as a trickle bed reactor.
7. The process according to claim 1, wherein said imination reaction is
carried out in a fixed bed reactor having a bed of fixed bed imination
catalyst arranged above a bed of fixed bed hydrogenation catalyst and the
reactor is operated as a trickle bed reactor.
8. The process according to claim 1, wherein said aminating hydrogenation
is carried out at a temperature in the range from 90.degree. to
130.degree. C. and a pressure in the range from 5 to 8 MPa.
9. The process according to claim 1, wherein a mixture consisting mainly of
10 to 40 wt. % of said cyclohexanone 10 to 40 wt. % of ammonia and
methanol are fed to the imination reaction.
10. The process according to claim 1, further comprising mixing said
cyclohexanone, ammonia and alcohol together in a reaction to form an
essentially homogeneous solution.
11. The process according to claim 1, further comprising said second step
produces a reaction mixture which is treated by distillation to obtain a
high-boiling fraction with a higher boiling point than isophorone diamine
and containing 3,5,5-trimethyl-6-imino-7-aza-bicyclo-›3,2,1!-octane
(=amidine) which is fed to said first stage together with a solution
containing isophorone nitrile, ammonia and methanol to enable continuous
operation.
Description
INTRODUCTION AND BACKGROUND
The present invention relates to an improved process for producing
3-aminomethyl-3,5,5-trimethylcyclohexyl amine, also referred to below as
isophorone diamine or IPDA, from 3-cyano-3,5,5-trimethylcyclohexanone,
also referred to below as isophorone nitrile or IPN.
In a further aspect, the present invention relates to a process comprising
a first stage for the at least partial conversion of isophorone nitrile
into isophorone nitrile imine and a second stage for the aminating
hydrogenation of the reaction mixture of the first stage with hydrogen and
ammonia in the presence of a lower alcohol and a fixed bed hydrogenating
catalyst based on Raney cobalt. The process according to the invention
permits the continuous production of isophorone diamine in high purity
with higher yield and/or higher space-time yield than prior known
two-stage processes.
Isophorone diamine has a number of significant utilities, including as a
starting product for the production of isophorone diisocyanate systems,
which is an isocyanate component for polyurethane systems as an amine
component for polyamides and as a hardener for epoxy resins. Isophorone
diamine is produced conventionally from isophorone nitrile, in which the
carbonyl group is converted into an amino group and the nitrile group into
an aminomethyl group in the presence of ammonia, hydrogen and conventional
hydrogenation catalyst. The starting product isophorone nitrile can be
obtained in conventional manner by the addition of hydrogen cyanide to
isophorone; see German published application 39 42 371 corresponding to
U.S. Pat. No. 5,091,554.
According to the process for producing isophorone diamine from isophorone
nitrile described in U.S. Pat. No. 3,352,913, the hydrogenation takes
place in the presence of ammonia and in the presence of known catalyst;
i.e. cobalt-, nickel-, iron-, or noble metal-containing catalysts at
50.degree. to 150.degree. C. and a pressure of at least 50 bar. For
example, the hydrogenation takes place in the presence of methanol as
solvent with the use of suspended and fixed bed catalysts. In addition to
the desired isophorone diamine, large amounts of by-products are also
obtained, e.g. in particular 3-aminomethyl-3,5,5-trimethylcyclohexylanol
(isophorone amino alcohol, IPAA). The low yield and the considerable
proportion of by-products formed in the known methods proved to be
disadvantages of this system.
In an attempt to obtain a higher yield of IPDA and to minimize the
unavoidable incidence of IPAA, the German published application 30 11 656
reveals a two-stage process, in which in the first stage IPN is converted
catalyst-free with surplus ammonia into
3-cyano-3-5,5-trimethyl-iminocyclohexane and the latter is then
hydrogenated to IPDA in the second stage. A disadvantage of this process
is that in addition to the actual hydrogenation reactor a special imine
formation reactor is required.
According to EP-B 0 042 119 it is regarded as a further improvement of the
known process to subject the isophorone nitrile, prior to the reaction of
the latter with ammonia and hydrogen in the presence of hydrogenation
catalysts at temperatures of 10.degree. to 120.degree. C. and pressures of
1 to 300 bar, to a preliminary reaction with ammonia in the presence of
inorganic and organic ion exchangers in the ammonium form as imine
formation catalysts. Whereas the ratio by volume of isophorone nitrile to
ammonia is to vary between 1 and 0.5 to 20 in the imine formation stage,
this ratio is increased to between 1 and 10 to 20 in the hydrogenation
stage. Although the process, which can be carried out in trickle bed
reactors, certainly leads to a high yield of IPDA and to a high purity,
the profitability of the process is impaired by the high surplus of
ammonia, which requires a very high pressure and hence makes sophisticated
hydrogenation equipment necessary.
According to German application 44 26 472 of DuPont it is also possible for
isophorone nitrile to be converted with the use of a supported heteropoly
acid catalyst with ammonia into the isophorone nitrile amine and for the
latter to be converted into isophorone diamine with the use of
conventional fixed bed hydrogenation catalysts, including also Raney.RTM.
cobalt. The high hydrogenating pressures required in practice--for example
238 bar--are disadvantageous, which calls for highly sophisticated
equipment.
In EP-B 0 042 19 a comparative example is also disclosed in which
isophorone nitrile and liquid ammonia are pumped from above into a fixed
bed hydrogenation reactor charged with commercial cobalt catalysts. The
reaction system is held at 270 bar with H.sub.2. There is obtained with
this single-stage form of execution, despite roughly quantitative
conversion of the isophorone nitrile, after working up by distillation
only 48% of isophorone diamine together with many by-products. According
to German application 43 43 890 corresponding to U.S. Pat. No. 5,504,254
the pressure was able to be reduced to 3 to 10 MPa by the use of a C.sub.1
--to C.sub.3 -- alcohol as solvent. With a trickle bed method of operation
a yield of just under 90% was achieved with an LHSV value of 1h.sup.-1
(liquid hourly space velocity) and without recycling of recrackable
high-boiling by-products.
A further two-stage process for producing isophorone diamine is known from
EP-A 0 449 089: in two reaction chambers physically separated from one
another a solution of isophorone nitrile is first of all reacted in
tetra-hydrofuran with surplus ammonia on acid metal catalysts and the
reaction mixture is hydrogenated in a second reaction chamber with
hydrogen in the presence of surplus ammonia on cobalt-, nickel-,
ruthenium- and/or other noble metal-containing catalysts and optionally
basic components at very high pressure. The high pressure makes very
sophisticated hydrogenation equipment necessary.
EP-A 0 394 967 also covers the production of isophorone diamine from
isophorone nitrile, wherein IPN is first of all converted into the
aminonitrile under conditions of reduced amination in the presence of a
first hydrogenation catalysts at moderate temperatures and the nitrile
group is then converted into an aminomethyl group at higher temperature in
the presence of a second hydrogenation catalyst having a hydrogenating
effect towards nitrile groups. Although this process can be carried out at
low pressures, it is regarded as a major disadvantage that a strict
temperature regime has to be observed during the two reaction stages, as a
result of which the space-time yield and hence the profitability of the
process decline. Unless special promoters are additionally used, the IPDA
product excessively high content in
3-cyano-3,5,5-trimethylaminocyclohexane, which is impossible to separate
by distillation.
In the process according to JP-A 06-321870 an equilibrium mixture of
isophorone nitrile imine obtained from isophorone nitrile in the absence
of an imination catalyst, but in the presence of methanol and ammonia, is
subjected to aminating hydrogenation in the presence of a fixed bed
catalyst containing a catalyst metal from the series Co, Ni, Ru and Pd
preferably Co on diatomite. The yield in IPDA is only 88%, and in addition
the space-time yield is low. According to JP-A 07-188126 use is made in
the aforementioned process for the aminating hydrogenation of a fixed bed
catalyst based on Raney cobalt, wherein the catalyst is obtained by the
elimination by melting of aluminum out of a binary or ternary Raney alloy.
In this case also the yield of IPDA given in the examples comes to only
some 88%.
An object of the present invention is to obtain a higher yield of IPDA
and/or higher space-time yield in a two-stage process for producing IPDA
and IPN. It is a further object to obtain IPDA in high product purity.
A still further object of the present invention is to carry out the
hydrogenation stage at a pressure of not more than 10 MPa, preferably
below 8 MPa, in order to keep the cost of equipment as low as possible.
SUMMARY OF THE INVENTION
The above and other objects are achieved by a process for producing
3-aminomethyl-3,5,5-trimethylcyclohexyl amine (isophorone diamine, IPDA)
from 3-cyano-3,5,5-trimethylcyclohexanone (isophorone nitrile, IPN),
comprising a first stage, in which isophorone nitrile is in the presence
or absence of an imination catalyst converted with ammonia at least
partially into 3-cyano-3,5,5-trimethylcyclohexanone imine, and a second
stage, in which the reaction mixture of the first stage, not yet present
on the whole, is, after the addition of an alcohol with 1 to 3 carbon
atoms, subjected to aminating hydrogenation with hydrogen with the use of
a fixed bed, special hydrogenation catalyst based on Raney cobalt at a
temperature in the range from 50.degree. to 150.degree. C. and a pressure
in the range from 3 to 10 MPa.
It is a feature of the present invention that the hydrogenation catalyst to
be used is produced by a process comprising:
(i) intimately mixing at least one powdery cobalt alloy and powdery cobalt
as binder, wherein the cobalt alloy contains cobalt and optionally
promoters as well as a leachable alloy component from the series aluminum,
zinc and silicon and the powdery mixture contains cobalt and leachable
alloy components in the ratio by weight of between 30 to 70 and 75 to 25,
(ii) sintering the powdery mixture to a mechanically stable molded product
with a density of 1.3 to 5.5 g/cm.sup.3, a pore volume up to 0.5 c.sup.3
/g (water adsorption) and a BET surface area (DIN 66 132) of less than 1
m.sup.2 /g and
(iii) activating the sintered molded product by at least partially leaching
out of the leachable alloy component by means of an alkali hydroxide
solution.
DETAILED DESCRIPTION OF INVENTION
The fixed bed catalyst to be used according to the invention for the
aminating hydrogenation of the reaction mixture obtained from the first
stage and containing isophorone nitrile imine and isophorone nitrile is
obtainable by the process described in German 43 35 360 (U.S. Pat. No.
5,536,694) and German 43 45 265 (U.S. Pat. No. 5,536,694). As regards the
selection and physical characteristics of the raw materials to be used in
the production--catalyst metal, alloy and, where required, promoters and
auxiliary substances such as molding aids, lubricants, plasticizers and/or
pore formers--and physical characteristics of the catalyst precursor as
well as details of the process stages, namely mixing of the components,
sintering of the powder mixture to moldings of the catalyst precursor and
activation of the catalyst by at least partial leaching of the leachable
alloy component out of the catalyst precursor, reference is made to the
above-mentioned documents which are relied on and incorporated herein by
reference for all relevant details.
There is given as the area of use for the catalysts described in the
aforementioned documents U.S. Pat. No. 5,536,694 and U.S. Pat. No.
5,536,694 the hydrogenation of nitro groups, C--C double bonds, sugars and
aromatic rings. Indications or a suggestion that imines and nitrile groups
should also be subjected to aminating hydrogenation with these catalysts
cannot be derived from the above-mentioned documents. It was surprising
that the use of these special fixed bed catalysts based on Raney cobalt in
the two-stage process according to the invention for producing IPDA from
IPN leads to a higher yield with in most cases even simultaneously higher
space-time yield. It was also found that corresponding catalysts based on
Raney nickel are considerably less effective in the two-stage production
of IPDA from IPN than those based on cobalt. Compared also with Raney
cobalt fixed bed catalysts previously used, the catalysts used according
to the invention showed a significantly higher catalyst effectiveness in
the second stage.
In the first stage of the process according to the invention at least one
part, preferably the greatest part, of the isophorone nitrile introduced
is converted into isophorone nitrile imine. The reaction mixture leaving
the imination stage should as far a8 possible contain isophorone nitrile
imine and isophorone nitrile in a molar ratio of more than 1. The
imination of the isophorone nitrile is conducted with expediency up to a
conversion rate of over 80%, preferably 90%.
If the imination is carried out in the absence of an imination catalyst,
several hours are required at a reaction temperature in the range between
10.degree. and about 60.degree. C. to achieve the desired imination rate;
although it is certainly also possible for the imination to be carried out
in the example at 100.degree. C. However, there is then the risk of an
increased formation of by-products, as a result of which the product
purity of the isophorone diamine obtained from the reaction mixture of the
second stage after recovery by distillation is adversely affected. It is
advisable to use an imination catalyst in order to accelerate the
establishment of equilibrium in the first stage. The imination catalyst
known from the prior art can be used for this. Suitable imination
catalysts, which is a well known term in the art, are acid inorganic and
organic ion exchangers (see EP-B 0 042 119), acid metal oxides, such as in
particular aluminum oxide and titanium oxide (anatase) (see EP-A 0 449
089), supported heteropoly acids (see German 44 26 472) and acid zeolites.
If an imination catalyst is used, the reaction temperature can lie in the
range between 10.degree. and 150.degree. C., preferably between 60.degree.
and 130.degree. C. and in particular between 80.degree. and 120.degree. C.
Although the imination of isophorone nitrile with liquid ammonia in the
absence of a further solvent is possible, it has proved to be advantageous
to use additionally an organic solvent from the series of an alcohol with
1 to 3 carbon atoms, preferably of a monovalent primary alcohol and in
particular methanol. Preferably there is fed to the imination reactor a
mixture containing isophorone nitrile, liquid ammonia and methanol. The
mixture contains 10 to 40 wt. %, preferably to 10 to 30 wt. %, of
isophorone nitrile and 10 to 40 wt. %, preferably 20 to 40 wt. %, of
ammonia. It is advantageous to mix isophorone nitrile, ammonia and the
alcohol together in a ratio such that an essentially homogeneous solution
is obtained. In principle the aforementioned limiting values for ammonia
and isophorone nitrile can also be fallen short of or exceeded, if an
essentially homogeneous solution is thereby obtained.
In the case of imination in the presence of an imination catalyst, the
catalyst can be used in the form of a suspended catalyst or a fixed bed
catalyst. The use of a fixed bed catalyst is advantageous, since elaborate
steps for the separation of the reaction mixture from the catalyst then
become superfluous. In the case of imination of isophorone nitrile in the
presence of a fixed bed catalyst the latter is employed in the form of
conventional catalyst moldings, such as extrusion moldings, pellets and
tablets, as a bed in a fixed bed reactor. The imination catalyst can be
arranged in its own reactor. It is also possible, however, to arrange the
imination catalyst in a reactor which contains both a bed of the imination
catalyst and a bed of the catalyst used for the aminating hydrogenation.
Depending on whether the reactor is operated as a trickle bed reactor or
as a bubble reactor, the bed of the imination catalyst is located above
(trickle bed) or below (bubble reactor) the bed of the hydrogenation
catalyst. It has proved to be advantageous to use a single reactor which
contains a bed of the hydrogenation catalyst and a bed of the imination
catalyst; preferably such a reactor is operated in the form of a trickle
bed reactor. The mixture of isophorone nitrile, liquid ammonia and
alcohol, in particular methanol, is then supplied at the reactor head. In
these cases hydrogen advantageously flows into the reactor simultaneously
from above for the aminating hydrogenation.
In addition to the aforementioned components of the mixture to be fed to
the imination stage, the latter can contain additionally fractions with a
higher or lower boiling point than isophorone diamine from the recovery by
distillation of the reaction mixture drawn off from the trickle bed
reactor. Such fractions can also contain, in addition to residues of
isophorone diamine, by-products from which isophorone diamine again forms
under the reaction conditions. The yield in isophorone diamine can be
increased substantially by returning fractions of this kind into the
mixture to be used. It is particularly advantageous to feed to the trickle
bed reactor the fraction with a boiling point above isophorone diamine,
which in addition to residues of isophorone diamine contains
3,3,5-trimethyl-6-imino-7-azabicyclo-›3,2-1!-octane as main product,
together with the mixture of isophorone nitrile, ammonia and solvent. The
recycling of the fraction containing the above-mentioned by-product--a
bicyclic compound of amidine structure--makes it possible to considerably
increase the yield of isophorone diamine and hence to enhance the
profitability of the process. The fraction containing the cyclic amidine
can, if this is desired, also be added directly to the reaction mixture to
be fed to the second stage.
The catalyst used in the second stage of the process according to the
invention is a fixed bed catalyst. Conventional fixed bed reactors are
used to carry out this process stage. As already mentioned in connection
with the imination stage, the reactor can be operated both as a trickle
bed reactor and as a bubble column, although, as follows also from German
43 43 390, the trickle bed method of operation is preferred.
The layouts and arrangement of suitable reactors are known to those skilled
in this art. Thus, the fixed bed catalyst is arranged in a vessel in the
form of one or more beds; the reactor also possesses devices for
controlling the temperature of the catalyst beds, in order to ensure that
the desired temperature is maintained in the particular catalyst bed.
Instead of a single trickle bed reactor, several trickle bed reactors can
also be connected one behind the other, wherein the reaction mixture
leaving the first reactor is charged again at the head of the second
reactor. The trickle bed reactor or reactors also possess suitable devices
for charging the reaction mixture and the hydrogen, also devices for
distributing the liquid over the surface of the first catalyst bed and
finally suitable removal devices for the reaction mixture leaving the
reactor.
The aminating hydrogenation, i.e. the second reaction stage, is carried out
at a temperature in the range of 50.degree. to 150.degree., preferably
80.degree. to 150.degree. C. and most preferably 90.degree. to 130.degree.
C. The aminating hydrogenation takes place at a pressure in the range of 3
to 10 MPa, preferably at 5 to 8 MPa and in particular below 8 MPa. Due to
the above-mentioned moderate operating pressures, which are possible with
the use of the claimed mixtures of isophorone nitrile, ammonia and solvent
and the trickle bed method of operation under the claimed temperature
conditions, the investment needed is reduced and hence the profitability
increased compared with processes which require a high operating pressure.
By the specified pressure is meant the overall pressure, which is the sum
of the partial pressures of ammonia, hydrogen C.sub.1 --C.sub.3 --alcohol
and the other components of the reaction mixture.
The volume of fixed bed catalyst required for the second stage is
determined by the LHSV value (liquid hourly space velocity), which is
dependent on the operating pressure, the temperature and the catalyst
activity and must be adhered to in order to achieve as quantitative as
possible a conversion of the mixture containing isophorone nitrile imine
and isophorone nitrile imine and isophorone nitrile. The LHSV comes
conventionally to at least 0.5 h.sup.-1 and preferably lies in the range
above 0.5 h.sup.-1 to 3 h.sup.-1. It is an advantage of the process
according to the invention that a virtually quantitative conversion is
achieved, and IPDA can be obtained in high yield and high purity, with an
LHSV value of about 2 h.sup.-1, a reaction temperature in the range
between 90.degree. and 130.degree. C. and a pressure between 5 and less
than 8 MPa. The high LHSV value leads in addition to a high space-time
yield.
In the embodiment particularly preferred according to the invention, in
which a trickle bed reactor contains a lower bed of hydrogenation catalyst
and an upper bed of imination catalyst, the respective bed height is
adjusted to the corresponding catalyst activity. The skilled person in the
art can determine this activity and hence the bed height by means of
simply performed preliminary tests. It follows from the examples that if
titanium dioxide is used as imination catalyst, a bed height which comes
to about a quarter of that of the hydrogenation catalyst is sufficient.
The hydrogen required for the hydrogenation can be fed to the reactor
either in excess or in an amount such that no hydrogen has to be
discharged from the reactor and recycled. Preferably hydrogen is not fed
in excess, in order to avoid the technical complexities involved in the
separation of this excess, the condensation of the ammonia and solvent
contained in the latter, and the compression of the purified hydrogen and
recycling.
The process according to the invention is distinguished by its simplicity,
low investment volume, high yield, high space-time yield and high IPDA
product purity.
The following examples serve to illustrate the present invention.
EXAMPLE 1
A reaction tube operated as a trickle bed reactor was filled in the lower
region with 160 ml of hydrogenation catalyst and in the region lying above
the latter with 40 ml of imination catalyst. Titanium dioxide (titanium
dioxide P 25 of Degussa AG) in the form of 1 mm extrudates was used as
imination catalyst. Activated Raney cobalt catalyst, produced according to
German patent application 43 45 265.5, in the form of tablets 5 mm in
height and 3 mm in diameter, was used as hydrogenation catalyst. The batch
solution, which contained IPN and methanol, as well as liquid ammonia were
pumped into the reaction tube from above. The hydrogen was also introduced
into the reaction tube from above. The reaction temperature was held at
100.degree. by oil heater. The pressure was set at 6 MPa. The liquid was
collected in a separation vessel. The gas current at the reactor inlet was
adjusted so that the whole of the hydrogen was consumed.
The batch solution contained 24 wt. % of IPN and 76 wt. % of methanol. 260
ml/h of this batch solution and 140 ml/h of ammonia were mixed directly
prior to charging to the reactor and the mixture was pumped into the
reactor. The LHSV value therefore came to 2h.sup.-1.
According to the analysis of the product mixture a yield of 92.2% of
isophorone diamine (=IPDA), referred to IPN used, was obtained. In
addition 3% of 2-aza-4,6,6-trimethyl -bicyclo-3,2,1-octane (=bicyclic
compound) and 3.3% of 3,5,5-trimethyl-6-imino-7-aza-bicyclo-3,2,1-octane
(=amidine) were contained in the product mixture. A product purity of
99.8% was obtained after the distillation of the liquid product mixture.
Methyl-IPDA was detectable in a quantity of only 200 ppm.
It follows from a comparison with the following comparative examples 1 and
2 that the use of the hydrogenation catalyst according to the invention
leads by virtue of this higher hydrogenation activity to a surprisingly
high increase in the yield and space-time yield.
COMPARATIVE EXAMPLE 1
A reaction tube operated as a trickle bed was filled with 160 ml of
hydrogenation catalyst in the lower region and with 40 ml of imination
catalyst in the region lying above the latter. Whereas the imination
catalyst corresponded to that of Example 1 (TiO.sub.2 P 25 of Degussa AG),
there was used as hydrogenation catalyst a commercial supported cobalt
catalyst based on 50% cobalt on a silicate support (injection moldings of
4-5 mm diameter and height). The operating conditions pressure,
temperature, LHSV value, flow rate and concentration of the methanolic IPN
batch solution and flow rate of the liquid ammonia--corresponded to those
of Example 1.
According to the analysis of the product mixture a yield of 82% of IPDA was
obtained.
COMPARATIVE EXAMPLE 2
Comparative example 1 was repeated, the only difference being that the
liquid flow rates were changed: 130 ml/h of methanolic IPN batch solution
(24 wt. % IPN) and 70 ml/h of liquid ammonia were mixed directly prior to
charging to the reactor and the mixture was pumped into the reactor. The
LHSV value therefore came to 1 h.sup.-1.
According to the analysis of the product mixture a yield of 90.7% of IPDA
was obtained, referred to IPN used. In addition 4% of bicyclic compound
and 3.2% of amidine were contained in the product mixture. Distillation of
the product mixture produced a product purity of 99.8 GC-FL. %.
The increase in the yield which still lay below that of Example 1 according
to the invention, was unfortunately accompanied by a halving of the
space-time yield.
COMPARATIVE EXAMPLE 3
The conversion was carried out in a similar way to Example 1, but using
inert steel balls 2 mm in diameter instead of the TiO.sub.2 imination
catalyst. All the other test conditions conformed to Example 1.
According the analysis of the product mixture a yield of 73.7% of IPDA was
obtained.
This comparative example shows that in the absence of an effective
imination catalyst, but using an activated Raney cobalt catalyst according
to the invention as hydrogenation catalyst, only a moderate IPDA yield is
obtained.
EXAMPLE 2
A solution containing 15 wt. % of IPN, 30 wt. % of ammonia and 55 wt. % of
methanol was produced and stirred in a pressure vessel under the pressure
obtained for 24 h at 25.degree. C.; in this case isophorone nitrile (IPN)
was converted largely into isophorone imino nitrile (IPIN). This solution
was then pumped at 400 ml/h, corresponding to an LHSV value of 2 h.sup.-1,
through the reactor, which was filled with 160 ml of hydrogenation
catalyst according to the invention (as in Example 1) and 40 ml of inert
steel balls. According to the analysis of the product mixture a yield of
92.1% of IPDA was obtained. After distillation of the product mixture a
product purity of 99.78% IPDA was obtained.
EXAMPLE 3
In a reaction tube filled according to Example 1 the reaction--imination
with subsequent hydrogenation--was carried out as per Example 1, the only
difference being that an LHSV value of 1 h.sup.-1 was set. According to
the analysis of the product mixture a yield of 94.2% of IPDA was obtained,
referred to IPN used. In addition bicyclic compound and 1% of amidine were
contained in the product mixture.
The example shows that the yield in IPDA was able to be increased still
further by a lowering of the LHSV value (compared with Example 1).
Further variations and modifications will be apparent to those skilled in
the art and are intended to be encompassed by the claims appended hereto.
German priority application 195 40 191.3 is relied on and incorporated
herein by reference.
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